【简答题】How did you get here today? 2. What means of transportation do you usually take? 3. What’s the most popular means of transportation in your country? 4. In your opinion, what would be the most popular ...
【单选题】A heavy,thick-walled tube,usually steel,used between the drill pipe and the bit in the drill stem to weight the bit in order to improve its performance is called a ______.